1. Field of the Invention
The present invention relates to the field of display technology, and in particular to a light guide plate and a backlight module.
2. The Related Arts
Liquid crystal displays (LCDs) have a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and are thus of wide applications, such as mobile phones, personal digital assistants (PDAs), digital cameras, computer monitors, and notebook computer screens.
Most of the liquid crystal displays that are currently available in the market are backlighting liquid crystal displays, which comprise an enclosure, a liquid crystal panel arranged in the enclosure, and a backlight module mounted in the enclosure. The structure of a conventional liquid crystal panel is made up of a color filter (CF) substrate, a thin-film transistor (TFT) array substrate, and a liquid crystal layer arranged between the two substrates and the principle of operation is that a driving voltage is applied to the two glass substrates to control rotation of the liquid crystal molecules of the liquid crystal layer in order to refract out light emitting from the backlight module to generate an image. Since the liquid crystal panel itself does not emit light, light must be provided from the backlight module in order to normally display an image. Thus, the backlight module is one of the key components of the liquid crystal displays. The backlight modules can be classified in two types, namely a side-edge backlight module and a direct backlight module, according to the location where light gets incident. The side-edge backlight module comprises an LED light bar, serving as a backlight source, which is arranged at an edge of a backplane to be located rearward of one side of the liquid crystal display panel. The LED light bar emits light that enters a light guide plate (LGP) through a light incident face at one side of the light guide plate and is projected out of a light exit face of the light guide plate, after being reflected and diffused, to pass through an optic film assembly so as to form a planar light source for the liquid crystal panel.
In a small-sized display device, to achieve a thinning design, it is often to cut down a thickness of the light guide plate. When a light emission surface of an LED light bar is arranged to have a width greater than the thickness of the light guide plate, a major portion of the light may become ineffective and thus, a wedge port must be provided at one side of the light incident surface of the light guide plate. Referring to FIG. 1, a cross-sectional view is given to illustrate a conventional light guide plate. The light guide plate comprises a first end surface 100, a second end surface 400 opposite to the first end surface 100, an upper surface 200 connected to upper edges of the first end surface 100 and the second end surface 400, and a lower surface 300 connected to lower ends of the first end surface 100 and the second end surface 400. The first end surface 100 and the second end surface 400 are both planar surfaces. The upper surface 200 is composed of three sections, which are respectively a first horizontal surface 210, a first slope surface 220, and a second horizontal surface 230. The first horizontal surface 210 is connected to the first end surface 100. The first slope surface 220 is connected, at an inclination, between the first horizontal surface 210 and the second horizontal surface 230. The lower surface 300 is, in the entirety thereof, a planar surface. The first end surface 100 is a light incident surface of the light guide plate. The second horizontal surface 230 is a light exit surface of the light guide plate.
A reference plane (indicated by a phantom line) extends from a connection point A between the first slope surface 220 and the second horizontal surface 230 to the lower surface 300. The portion of the light guide plate from the reference plane to the first end surface 100 is a light incident portion. The light incident portion of the light guide plate comprises a wedge body. The portion of the light guide plate from the reference plane to the second end surface 400 is a light guide portion. The light guide portion of the light guide plate is generally a rectangular parallelepiped. The light guide portion of the light guide plate has a thickness that is generally smaller than a thickness of the light incident portion of the light guide plate.
Arranging the light incident portion of the light guide plate in a structure of a wedge body can address the issue of ineffective light caused by a width of a light emission surface of an LED light bar being greater than a thickness of a light guide plate. Light, after entering the light incident portion of the light guide plate, is subjected to total internal reflection on the first slope surface 220 to transmit into the light guide portion of the light guide plate and then reflected by a reflector plate below the light guide plate to project out through the second horizontal surface 230.
However, with further progress of thinning of light guide plates, the thickness of the light guide portion of a light guide plate becomes thinner and thinner and a difference of thickness between the light incident portion and the light guide portion of the light guide plate becomes larger. As shown in FIG. 2, the slope of the first slope surface 200 becomes larger, making it not possible for a fraction of light that is of a large angle to transmit into the interior of the light guide plate for utilization thereby lowering down the utilization of light. For backlight modules that are of severe degree of thinning, loss of light at the light incident portion of the light guide plate is severer and some of the light becomes stray light that enters the area of an optic film assembly above the light guide plate, leading to the occurrence of bright edges. Thus, providing only a light incident portion having a structure of a wedge body on a light guide plate is just not enough to achieve an ideal light coupling efficiency.